U.S. patent number 4,110,810 [Application Number 05/776,231] was granted by the patent office on 1978-08-29 for static charge neutralizer and process.
This patent grant is currently assigned to E. I. Du Pont de Nemours and Company. Invention is credited to Edward J. Moore, John E. Owens.
United States Patent |
4,110,810 |
Moore , et al. |
August 29, 1978 |
Static charge neutralizer and process
Abstract
A device is disclosed for neutralizing static charge generated
in a moving web of dielectric material. A conductive bare wire is
impressed with an AC voltage of 3000 to 10,000 volts at a frequency
of 40-70 Hertz and located near the web.
Inventors: |
Moore; Edward J. (Florence,
SC), Owens; John E. (Hockessin, DE) |
Assignee: |
E. I. Du Pont de Nemours and
Company (Wilmington, DE)
|
Family
ID: |
27669621 |
Appl.
No.: |
05/776,231 |
Filed: |
March 10, 1977 |
Current U.S.
Class: |
361/213 |
Current CPC
Class: |
H05F
3/04 (20130101) |
Current International
Class: |
H05F
3/00 (20060101); H05F 3/04 (20060101); H05F
003/04 () |
Field of
Search: |
;361/212,213,214,220
;250/326,324 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Goldberg; Gerald
Claims
What is claimed is:
1. A web winding device for a dielectric web material
comprising:
a driven winding roll onto which the web is wound;
a nip roll in pressure contact with the web wound on the winding
roll and at which pressure contact the web is first laid onto the
winding roll;
a conductive bare wire less than 0.03 cm in diameter extending
across and parallel with the web and located 0.6 to 8 cm from the
web on the winding roll in an arc of 0.degree. to 90.degree. after
contact by the web with the winding roll; and
means for impressing an AC voltage on the wire of 3000 to 10,000
volts at 40 to 70 Hertz.
2. The device of claim 1 wherein the wire is greater than 0.010 cm
in diameter.
3. The device of claim 1 wherein the wire is 1.25 to 5 cm from the
web.
4. The device of claim 1 wherein the AC voltage is 6000 to 9000
volts.
5. The device of claim 1 wherein the wire is located in an arc of
0.degree. to 45.degree. after contact by the web with the winding
roll.
6. The device of claim 1 wherein there is a grounded conductor,
coextensive and parallel with the bare wire located 0.6 to 8 cm
from the web away from the bare wire in the direction of web
travel.
7. The device of claim 6 wherein the grounded conductor is 1.25 to
5 cm from the web.
8. A static charge neutralizing device for dielectric web material
comprising:
means for continuously moving the web material in a predetermined
path;
conductive bare wire less than 0.03 cm in diameter extending across
and parallel with the web material and located 0.6 to 8 cm from the
web material; and
means for impressing an AC voltage on the wire of 3000 to 10,000
volts at 40 to 70 Hertz.
9. The device of claim 8 wherein the wire is greater than 0.010 cm
in diameter.
10. The device of claim 8 wherein the wire is 1.25 to 5 cm from the
web material.
11. The device of claim 8 wherein the AC voltage is 6000 to 9000
volts.
12. The device of claim 8 wherein there is a grounded conductor,
coextensive and parallel with the bare wire, located 0.6 to 8 cm
from the web away from the bare wire in the direction of web
travel.
13. The device of claim 12 wherein the grounded conductor is 1.25
to 5 cm from the web material.
14. A process for continually neutralizing static charge on
dielectric web material comprising:
moving the web material in a predetermined path 0.6 to 8 cm from a
conductive bare wire less than 0.03 cm in diameter extending across
and parallel with the web material and
impressing an AC voltage on the wire of 3000 to 10,000 volts at 40
to 70 Hertz.
15. The process of claim 14 wherein the wire is greater than 0.010
cm in diameter.
16. The process of claim 14 wherein the wire is 1.25 to 5 cm from
the web material.
17. The process of claim 14 wherein the AC voltage is 6000 to 9000
volts.
18. The process of claim 14 comprising the additional step of
moving the web material 0.6 to 8 cm from a grounded conductor
coextensive and parallel with the bare wire and located away from
the bare wire in the direction of web travel.
19. A process for winding and continually neutralizing static
charge on dielectric web material comprising:
moving the web material onto a winding roll between the winding
roll and a nip roll in pressure contact therewith and 0.6 to 8 cm
from a conductive bare wire less than 0.03 cm in diameter extending
across and parallel with the web material and located in an arc
around the winding roll of 0.degree. to 90.degree. after contact by
the web material with the winding roll and
impressing an AC voltage on the wire 3000 to 10,000 volts at 40 to
70 Hertz.
20. The process of claim 19 wherein the wire is greater than 0.010
cm in diameter.
21. The process of claim 19 wherein the wire is 1.25 to 5 cm from
the web material.
22. The process of claim 19 wherein the AC voltage is 6000 to 9000
volts.
23. The process of claim 19 comprising the additional step of
moving the web material 0.6 to 8 cm from a grounded conductor
coextensive and parallel with the bare wire and located away from
the bare wire in the direction of web travel.
24. The process of claim 19 wherein the wire is located in an arc
around the winding roll of 0.degree. to 45.degree..
Description
Handling webs of dielectric film material generates static electric
charge in the material. Such static charge causes difficulty in
further processing such as in rolling, slitting or using the web.
Neutralization of static charges on the surface of moving webs of
film material has long been a goal of workers in this field.
Charge neutralizing devices have been disclosed wherein fine wire
electrodes are located in proximity to the web material to be acted
upon. U.S. Pat. No. 777,598 discloses removal of static charge by
transport of a web of dielectric material past a wire electrode
having a high electrical potential. Voltage impressed on the wire
electrode is disclosed to be high enough to spark across about
three-quarters of an inch. The voltage is generated by a Tesla coil
at the high frequency characteristic of such a device.
U.S. Pat. No. 983,536 discloses a static neutralizing device
wherein an insulated conductor with large surface area is
positioned over a moving web of dielectric material and is
impressed with a high AC voltage. The voltage is disclosed to
create an electrostatic field through which the web material is
passed and in which is located an uninsulated fine wire ground
conductor. The ground conductor is required for operation of the
device.
U.S. Pat. No. 3,364,726 discloses a static neutralizing device
wherein an insulated fine wire electrode is impressed with AC
voltages at various frequencies ranging from 300 to 2000 Hertz
depending upon the speed of the web material to be neutralized. The
fine wire electrode is required to be positioned very near to the
moving web and there is also a requirement for a conductive
metallic ground bar to be positioned nearby.
This invention relates to neutralizing static charges on a fast
moving web of dielectric material. The neutralizing is accomplished
by impressing an alternating current (AC) voltage at a low
frequency on a fine conductive bare wire located near to the moving
web. Such an arrangement permits successful high speed operation
using a low frequency voltage source. Accordingly, there is
provided a static charge neutralizing device for dielectric web
material comprising means for continuously moving the web material
in a predetermined path; conductive bare wire less than 0.030 cm
(12 mils) in diameter extending across and parallel with the web
material and located from 0.6 to 8.0 cm (1/4 to 3 inches) from the
web material; and means for impressing an AC voltage on the wire of
from 3000 to 10,000 volts at 40 to 70 Hertz.
As applied specifically to winding rolls of dielectric web
material, there is provided a web winding device for a dielectric
web material comprising a driven winding roll onto which the web is
wound; a nip roll in pressure contact with the web wound on the
winding roll and at which point of pressure contact the web is
first laid onto the winding roll; a conductive bare wire less than
0.030 cm (12 mils) in diameter extending across and parallel with
the web and located from 0.6 to 8.0 cm (1/4 to 3 inches) from the
web material on the winding roll in an arc of 0.degree. to
90.degree. after contact by the nip roll; and means for impressing
an AC voltage on the wire of from 3000 to 10,000 volts at 40 to 70
Hertz.
The invention includes a process for continually neutralizing
static charge on dielectric film material comprising moving the web
material in a predetermined path 0.6 to 8.0 cm (1/4 to 3 inches)
from a conductive bare wire less than 0.030 cm (12 mils) in
diameter extending across and parallel with the web material, and
impressing an AC voltage on the wire of from 3000 to 10,000 volts
at 40 to 70 Hertz.
Important and critical elements in operation of the present
invention include the use of a fine bare, conductive wire impressed
with an AC, low frequency, voltage adequate to initiate corona
discharge but not exceeding that which will cause sparking.
FIG. 1 is a representation of the relation between the fine wire
electrode of this invention and a moving web and an optional
grounded conductor.
FIG. 2 is a representation of this invention as it relates to a
slit web winding device.
Referring to FIG. 1, web of dielectric material 10 is moved in the
direction of the arrow and is wound onto take-up roll 11. The web
10, by virtue of its handling history bears an electrostatic charge
prior to passing under fine wire electrode 12. Wire electrode 12 is
located parallel with the surface of web 10, is spaced 0.6 to 8.0
cm (1/4 to 3 inches) from web 10, and extends thereacross.
Electrode 12 bears an electrical potential impressed from
transformer source 13a having, for example, a primary side powered
by a 110 volt AC at 60 Hertz to a secondary side providing 3000 to
10,000 volts. Voltage to transformer source 13a is supplied from
commercial line current and can be controlled or adjusted by means
of a variable voltage transformer 13b. The voltage on electrode 12
is adjusted to be less than that voltage which would cause
spontaneous spark discharge but more than the voltage required to
initiate corona discharge. Optional, grounded conductor 14 is
located parallel and coextensive with electrode 12 and is spaced
0.6 to 8.0 cm (1/4 to 3 inches) from web 10 and about 0.6 to 8.0 cm
(1/4 to 3 inches) from electrode 12.
Referring to FIG. 2, slit web 15" moves around platen roll 16 and
individual webs 15 and 15' advance to nip rolls 17 carried on
pivotal arms 18 (equivalent elements on the right hand winding
assembly are not numbered). The nip rolls 17 make pressure contact
with wind-ups 19 wound on cores 20 and individual webs 15 and 15'
are rolled onto the wind-ups. Electrostatic charge is generated
when the dielectric web moves past a roll 16 or through nips 21. To
make a charge neutralized wind-up, the charge should be continually
neutralized at a location on the wind-up between the nips 21 and
points around the wind-ups 22 less than 90.degree. from the nip.
Neutralization of the charge is accomplished within the angle to
avoid establishment of a charge of reversed polarity on the wind-up
surface. Prompt neutralization does not give time for establishment
of such charges. It is preferred that the charge should be
neutralized within an angle of 9.degree. to 45.degree. from the
nip. In FIG. 2, wire electrodes 12 and 12' and grounded conductors
14 and 14' are diagrammatically shown to be located within the
preferred 45.degree. angle. Voltage source and ground connection
for wire electrodes and grounded conductors are similar to those of
FIG. 1. Wire electrodes and grounded conductors are mounted to
pivotal arms 18. As wind-ups 19 increase in size, the electrodes
and the conductors remain approximately the same distance from the
periphery of the wind-ups.
This invention can be used to neutralize static charge on any
moving web of dielectric material. Examples of such material
include fibrous materials such as paper, fabrics, spun-bonded
synthetics and the like and nonfibrous materials such as
regenerated cellulose, films of synthetic polymers, and the like.
The invention is used to particular advantage on webs of polyester,
polyimide, and polyolefin film material. Such synthetic polymeric
materials show a high degree of static charge retention and this
invention, with its improved static charge neutralization, provides
particularly good results. The invention has been found to operate
especially effectively on webs of polyethylene terephthalate.
The fine wire electrode can be made from any conductive material of
suitable tensile strength. Stainless steel is preferred. The wire
must be bare and care must be exercised to keep the wire free from
insulating contamination during operation. The bare wire is
necessary because it must discharge ions on contact and, to the
extent that the wire is insulated, ions cannot make contact with
it. The fine wire electrode is generally of round cross section but
such is not necessary. The wire should be of a diameter less than
about 0.030 cm (12 mils) and less than about 0.025 cm (10 mils) is
preferred. The charge neutralizer operates more effectively as the
wire diameter is reduced, however, the lower limit for wire
diameter is a matter of the tensile strength of the wire. The wire
diameter should be large enough at the tensile strength of the wire
material selected, to permit taut spans of wire across the web of
material. The wire is usually greater than 0.010 cm (4 mils) in
diameter.
The grounded conductor is optional to practice of this invention,
however, when used results are somewhat improved. The ground is
located away from the fine wire electrode in the direction of web
travel and can be a rod of conductive material. Uninsulated
stainless steel rod about one-fourth inch in diameter has been used
with good results. A grounded conductor is useful to ensure that a
ground exists on the same side of the moving web as the fine wire
electrode. It is important that some ground is present during
static charge neutralization and that it is located in an
unobstructed line from the fine wire electrode.
The voltage source is commercial AC, generally 60 Hertz, adjusted
by means of a transformer. Voltage is established at a level which
is adequate to initiate corona discharge. Because the fine wire
electrode is bare and substantially unshielded, the corona
discharge subtends a wide angle of influence and is capable of
neutralizing a relatively large band across the moving web of
material at any given instant. Operation of this invention is
effective on webs of material moving at least as fast as 11 m/sec
(700 yards per minute). There is no lower limit for web speed. The
invention effectively neutralizes a stationary web.
In neutralizing tests utilizing a slit web winding device similar
to that depicted in FIG. 2, wind-ups of polyethylene terephthalate
film material 25 to 100 cm (10 to 40 inches) wide and 6.25 to 50.0
microns (0.25 to 2.0 mils) thick have been made with a residual
static charge of less than 0.2 kilovolts at 5 cm (2 inches) from
the film surface. (Residual static charge values stated hereafter
are as determined 5 cm [2 inches] from the film surface). The fine
wire electrodes were a tantalum alloy 0.015 cm (6 mils) in
diameter. The tests were conducted at web speeds of 0-11 m/sec
(0-700 yards/min) with the wire electrodes charged to 7000 to 8000
volts at 60 Hertz and located an average of 2.5 cm (1 inch) from
the wind-up surface over the course of the winding process. When
voltage to the wire electrodes was shut off, the wind-ups increased
to a residual static charge of greater than 30 kilovolts. When the
fine wire electrodes were located beyond 90.degree. from the nip of
the winding device, the residual static charge on similar sized
wind-ups was greater than 8 kilovolts. The preferred distance for
wire electrodes and grounded conductors from the web material is
1.25 to 5 cm (1/2 to 2 inches).
In comparison neutralizing tests using the same electrode charging
voltage (6500 volts), fine wire electrodes 0.020 cm (8 mils) in
diameter resulted in wind-ups with 3 kilovolts residual static
charge; electrodes 0.015 cm (6 mils) in diameter resulted in
wind-ups with 1.5 kilovolts residual static charge; and electrodes
0.013 cm (5 mils) in diameter resulted in wind-ups with 0.3
kilovolts residual static charge.
In comparison neutralizing tests using 0.015 cm (6 mil) fine wire
electrodes, electrode potential voltage of 8000 volts resulted in
wind-ups with 0.3 kilovolts residual static charge and electrode
potential voltage of 6500 volts resulted in wind-ups with 1.5
kilovolts residual static charge. The preferred fine wire electrode
potential is 6000 to 9000 volts.
* * * * *